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Self build residential annexes

Extending your own home or building residential annexes within the grounds of your own home

Extending your own home

With effect from 06 July 2017 we no longer administer CIL on residential self build extensions. You only need to submit CIL forms if your extension is over 100 metres squared and you are not able to apply for the exemption.

What is a residential annex or extension?

CIL Regulation 42A states:

The development is a residential annex if it:

  • is wholly or mainly within the curtilage of the main dwelling; and
  • comprises of one new dwelling

The development is a residential extension if it:

  • is an enlargement to the main dwelling; and
  • does not comprise of a new dwelling

Exemptions from the levy

People who extend their own homes within the grounds of their own homes are exempt from the levy, provided that they meet the following criteria:

  • the main dwelling must be the self builder's main residence, and they must have a material interest (own or have a leasehold of seven years or more in it)
  • building work on the extension or annex has not already started or been completed before the planning application is submitted

Residential extensions under 100 square metres are also exempt from the levy.

How to claim for exemption

Please submit your claim for self build residential annex exemptions using the relevant form below:

You can email the form to us, or send it in the post (our contact details are at the bottom of the page).

Disqualifying event

In some cases, a disqualifying event may occur where the conditions for granting relief no longer apply. If such an event occurs within three years (from completion of development) we'll then 'clawback' any relief on the chargeable development. CIL will become payable in full.

Disqualifying events include:

  • using the main house for a purpose other than a single dwelling
  • letting out the annex or the main residence
  • selling either the main dwellings or the annex separately from the other
  • sell or rent out your home within three years of the house being completed

If a disqualifying event occurs you must notify us in writing within 14 days of the event. If this is not done, a surcharge will be applied in addition to the levy.

Important information

It is important that you do not begin work until you submit your application for exemption and you receive notice from us with a decision.

Your application for exemption will be refused if you start any work, including digging foundations.

You will be required to pay the full amount of CIL if:

  • you fail to submit a commencement notice before starting any work (this must be submitted and received by us at least one day before starting any work)

We can also impose surcharges, in addition to the full CIL charge.


Please contact the CIL Officer on 01553 616443 if you have any questions or disagree with any aspect of the CIL prior to making an appeal.

You have the right to appeal against a grant of relief to the Valuation Office Agency.